Engine piston

ABSTRACT

The baffle on the piston for a two-cycle engine has a sharp upper edge formed by an obtuse angle and a crowned top constructed to prevent overheating and destruction of the upper edge of the baffle.

United States Patent Charles F. Alexander, Jr. Oshkosh, Wis. 7 856,584

Sept. 10, 1969 Aug. 24, 197 l Brunswick Corporation Chicago, Ill.

lnventor Appl. No. Filed Patented Assignee ENGINE PISTON 8 Claims, 7 Drawing Figs.

u.s.c1 92/141, 123/193 P 1m. 01 F02f3/24 Fie1d ofSearch 92/141,

Primary Examiner-Martin P. Schwadron Assistant ExaminerA1len M. Ostrager Attorney-Roy T. Montgomery ABSTRACT: The baffle on the piston for a two-cyc1e engine has a sharp upper edge formed by an obtuse angle and a crowned top constructed to prevent overheating and destruction of the upper edge of the baffle.

Patented Aug. 24, 1971 FIG FIG 3 INVENTOR. CHARLES E ALEXANDER JR 7 M git A ttorneys ENGINE PISTON This invention relates to an engine piston having a baffle or deflector to guide the flow of intake gases entering from a port or ports in the side of the cylinder.

As described in US. Pat. No. 2,512,739 to Lane Duncan it is well known that baffles or deflectors on pistons in two-cycle engines are susceptible to undesirable melting leading to destruction and which may substantially shorten the useful life of a piston and/or reduce its efficiency.

It is particularly desirable to maintain the integrity of the sharp upper edge of the baffle or deflector facing the intake ports, as against melting or erosion which tends to destroy the sharpness of the edge and reduce the effectiveness of the baffle.

The present invention is based upon the discovery that by forming the sharp upper edge by an obtuse angle and properly crowning the upper surface of the baffle, additional material may be provided to conduct heat away from the sharp edge of the baffle thereby maintaining a safe temperature level to prevent destruction of the sharp edge. In constructing the baffle, it must be kept in mind that a sharp edge or very small radius must be maintained at the upper end of the deflector or baffle surface so that the incoming charge separates from the piston at this point and retains the flow direction induced by the baffle.

A large radius (one-sixteenth) inch radius on a 3-inch diameter piston) at the upper end of the deflector surface will cause a deflection of the incoming charge (by the well-known Coanda effect) toward the cylinder center which will reduce scavenging efficiency and consequently the horsepower produced.

The invention is illustrated in the accompanying drawings in which:

FIG. 1 is a vertical axial section of a piston and cylinder assembly showing one embodiment of the invention;

FIG. 2 is a top plan view of the piston of FIG. 1;

P16. 3 is an elevation of a piston partially sectioned and showing another embodiment of the invention;

FIG. 4 isa side plan view showing another embodiment of the invention;

FIG. 5 is a view similar to the piston in FIG. 1 showing another embodiment of the invention;

FIG. 6 is a side plan view illustrating a prior construction of baffle; and

FIG. 7 is a view similar to FIG. 6 showing what happens after the edge of the baffle of FIG. 6 softens or melts and becomes less sharp.

Referring to FIG. 6, it will be noted that the sharp corner edge 1 on the deflector guide or baffle 2 of piston 3 causes the incoming gases to separate from the piston at that point thereby retaining the flow direction initiated by the baffle. When the sharp upper edge 1 melts to a rounded shape as shown in FIG. 7, the incoming gases are diverted as shown (by the Coanda effect) and scavenging becomes less efficient with resultant loss of power.

It has been known for some time that in a construction like that of FIG. 6 the sharp upper corner edge 1 of the deflector or baffle has the highest temperature. For engines operated at high output the edge temperature becomes a power-limiting factor. Heretofore various attempts have been employed in trying to solve the problem as in the Duncan patent referred to above. and to thereby provide a longer useful life for the piston. In general these attempts have been costly in nature.

The present invention is based upon the discovery that by adding more metal at the top of the deflector or baffle it is possible to conduct the heat away from the sharp edge at an increased rate.

The invention changes the sharp edge from one having a 90 angle or less to one having an obtuse angle greater than 90, as shown in FIGS. 1, 3, 4, and 5. Since the highest temperatures are nearest the center of the combustion space in the cylinder,

it is possible that the angle of the sharp edge may be gradually reduced to 90 in the region of the ends of the baffle as shown in FIG. 4.

In FIG. 1 there is illustrated a typical baffle 4 on piston 5 in cylinder 6, and which baffle has a wall 7 generally parallel to the axis of the piston 5 and facing the inlet port 8 so that the incoming fuel air mixture rises above the baffle to the top of the cylinder in the scavenging process.

In carrying out the invention the baffle terminates in a sharp edge 9 formed by an obtuse angle and has a crown portion 10 behind the edge 9. The obtuse edge 9 and crown 10 form a heat conducting mass to keep the temperature of the sharp edge 9 down sufficiently to avoid melting or crumbling caused by loss of strength at high temperature.

The crown 10 is shown convex in section, but is is to be understood that it may take different shapes, the important characteristic being that an obtuse angle is provided at the sharp edge 9 to provide additional material to conduct heat from the upper edge of the baffle without interfering with the flow separation at that point. 7

Also, it is to be understood that, although the obtuse angle at the sharp edge 9 is shown formed by a straight line extending angularly rearwardly upwardly from the sharp edge, the angle could be formed by an arc and still be an obtuse angle at the sharp edge 9.

In FIG. 1 the sharp edge 9 is shown as about a 145 angle which is about the maximum angle which will still substantially avoid the Coanda effect.

In FIG. 3 the crown 11 is applied to a somewhat different type of guide 12, and in this instance the sharp edge 13 is shown as about a 120 angle.

In FIG. 4 the obtuse angle 14 of about 145 is in the central portion 15 of the baffle 16 and gradually decreases to about a right angle at the ends 17 thereof. Also, the top of the baffle has a' crown 18 at the central portion 15 which becomes nearly flat at the ends 17.

In FIG. 5 the piston 19 has a small obtusely angled step 20 providing a sharp edge 21 which causes the flow to separate from the edge 21 and, also, the additional material with the crown 22 to conduct heat away from the edge 21.

I claim:

1. A piston for a two-cycle internal combustion engine having an intake baffle thereon extending completely across a portion of the top of said piston, said baffle having a front face thereon substantially parallel to the axis of the piston for deflecting an incoming flow of gases, the improvement comprising a sharp upper edge terminating the front face of said baffle to maximize the gas separation from said baffle at said edge, said edge being formed by an obtuse angle with respect to said face.

2. The piston of claim 1 further comprising a crown portion on top of the baffle behind said sharp edge.

3. The piston claim 1 wherein said obtuse angle is less about 145.

4. The piston of claim 1 wherein said obtuse angle is about 5. A piston for a two-cycle internal cornbustionengine having a baffle thereon extending completely across a portion of the top of the piston, said baffle having a front face thereon substantially parallel to the axis of the piston for deflecting an incoming flow of gases, the improvement comprising a sharp upper edge terminating the front face of said baffle to maximize the gas separation from said baffle at said edge, said edge being formed by an obtuse angle with respect to said face at the central portion of said baffle larger than the angle at the ends thereof.

6. The piston of claim 5 further comprising a crown portion on top of the baffle behind said sharp edge at said central portion gradually reducing in height toward the ends thereof.

7. The piston of claim 5 wherein said obtuse angle is less than 8. The piston of claim 5 wherein said obtuse angle is about 120. 

1. A piston for a two-cycle internal combustion engine having an intake baffle thereon extending completely across a portion of the top of said piston, said baffle having a front face thereon substantially parallel to the axis of the piston for deflecting an incoming flow of gases, the improvement comprising a sharp upper edge terminating the front face of said baffle to maximize the gas separation from said baffle at said edge, said edge being formed by an obtuse angle with respect to said face.
 2. The piston of claim 1 further comprising a crown portion on top of the baffle behind said sharp edge.
 3. The piston claim 1 wherein said obtuse angle is less about 145*.
 4. The piston of claim 1 wherein said obtuse angle is about 120*.
 5. A piston for a two-cycle internal combustion engine having a baffle thereon extending completely across a portion of the top of the piston, said baffle having a front face thereon substantially parallel to the axis of the piston for deflecting an incoming flow of gases, the improvement comprising a sharp upper edge terminating the front face of said baffle to maximize the gas separation from said baffle at said edge, said edge being formed by an obtuse angle with respect to Said face at the central portion of said baffle larger than the angle at the ends thereof.
 6. The piston of claim 5 further comprising a crown portion on top of the baffle behind said sharp edge at said central portion gradually reducing in height toward the ends thereof.
 7. The piston of claim 5 wherein said obtuse angle is less than 145*.
 8. The piston of claim 5 wherein said obtuse angle is about 120*. 